/usr/lib/pkgconfig/ is in libgtkmathview-dev 0.8.0-9ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/pkgconfig/gtkmathview-custom-reader.pc
/usr/lib/pkgconfig/gtkmathview-gmetadom.pc
/usr/lib/pkgconfig/gtkmathview-libxml2-reader.pc
/usr/lib/pkgconfig/gtkmathview-libxml2.pc
/usr/lib/pkgconfig/mathview-backend-gtk.pc
/usr/lib/pkgconfig/mathview-backend-ps.pc
/usr/lib/pkgconfig/mathview-backend-svg.pc
/usr/lib/pkgconfig/mathview-core.pc
/usr/lib/pkgconfig/mathview-frontend-custom-reader.pc
/usr/lib/pkgconfig/mathview-frontend-gmetadom.pc
/usr/lib/pkgconfig/mathview-frontend-libxml2-reader.pc
/usr/lib/pkgconfig/mathview-frontend-libxml2.pc